Ralf Averbeck Department of Physics & Astronomy Seminar at Department of Chemistry Stony Brook University, October 17, 2005 Big Bang Chemistry Exploring the Properties of Primordial Matter at RHIC

Ralf Averbeck, 2 Stony Brook University, 10/17/2005 Outline l Introduction l Nuclear collisions at RHIC l Establishing the “final” state l Looking “inside” with penetrating probes l Direct photons l Jets l Heavy quarks l Electromagnetic radiation l Summary l Outlook

Ralf Averbeck, 3 Stony Brook University, 10/17/2005 “Chemistry” at many scales l what is Chemistry? Merriam-Webster dictionary: “a science that deals with the composition, structure, and properties of substances and with the transformations that they undergo“ l substances? l “biological” structures l complex “compounds” l molecules l atoms l nuclei & electrons l protons & neutrons l quarks & gluons l today’s topic l transformation of nuclear matter into quark-gluon matter l study of the properties of quark-gluon matter biology physics

Ralf Averbeck, 4 Stony Brook University, 10/17/2005 Nuclear matter as QCD laboratory l nuclear matter is made from nucleons: l 3 (light) constituent quarks, carrying color charge l quarks interact via gluon exchange l gluons carry color charge (“colored photons”)! l puzzles: l isolated quarks are NEVER observed (“confinement“) l quark masses account for ~1% of the nucleon mass l properties of the theory of strong interaction: QCD (Quantum Chromo Dynamics) l QCD vacuum is not empty

Ralf Averbeck, 5 Stony Brook University, 10/17/2005 The QCD phase transition l learn about fundamental properties of matter by l observing the QCD phase transition l investigating the properties of quark-gluon matter l but how? l look back at the first successful attempt of a QCD phase transition nuclear matterquark-gluon matter phase transition change of the relevant degrees of freedom l confinement l dynamically generated mass l asymptotic freedom l constituent mass

Ralf Averbeck, 6 Stony Brook University, 10/17/2005 A short history of the universe ~ 10  s after Big Bang Hadron Synthesis quarks & gluons → hadrons ~ 100 s after Big Bang Nucleon Synthesis protons & neutrons → nuclei Temperature increases Degrees of freedom are liberated

Ralf Averbeck, 7 Stony Brook University, 10/17/2005 The tools of the trade l how to excite matter to T ~ K (~200 MeV)? l heating by “brute force” l dump maximum energy into minimum volume l Relativistic Heavy Ion Collider: BNL STAR l 4 experiments study collisions l (polarized) p+p l A+A l A+B l with maximum energy in CMS l 500 GeV (p+p) l 200 GeV (A+A) per N-N pair!

Ralf Averbeck, 8 Stony Brook University, 10/17/2005 The PHENIX experiment l 3 detectors for event characterization l collision vertex? l centrality: peripheral or central? l orientation of the reaction plane? l 2 forward spectrometers l muons pseudo rapidity 1.2 < |  | < 2.4 momentum p  2 GeV/c l 2 central spectrometers l hadrons l electrons l photons pseudo rapidity  0.35 l momentum p  0.2 GeV/c

Ralf Averbeck, 9 Stony Brook University, 10/17/2005 The experimental challenge STAR l ONE central Au+Au collision at max. energy l production of MANY secondary particles PHENIX

Ralf Averbeck, 10 Stony Brook University, 10/17/2005 Critical energy density nuclear matter: p,n quark-gluon matter: q, g temperature and/or density distance between nucleons: 2 r 0 ~ 2.3 fm nucleon radius: r n ~ 0.8 fm l more sophisticated l QCD calculations on a discrete space-time lattice l phase transition for –critial temperature T C ≈ 170 MeV (10 12 K) –critical energy density  C ≈ 1 GeV/fm 3 naive estimate of critical energy density  c : l nuclear ground state critical: nucleons overlap

Ralf Averbeck, 11 Stony Brook University, 10/17/2005 Energy density reached at RHIC l more sophisticated: Bjorken model l relate  with measured transverse energy E T nuclear radius R ~ 6.5 fm formation time  ~ fm/c   BJ ~ 5 – 15 GeV/fm 3 very naive estimate of  l assume ALL energy dumped in volume of Au nucleus  = (197 x 200 GeV)/(4/3  R 3 Au ) ~ 34 GeV/fm 3 l lattice QCD relate  with T l  BJ = 5 – 15 GeV/fm 3 → T i = 250 – 350 MeV ,T  sufficient for QCD phase transition at RHIC

Ralf Averbeck, 12 Stony Brook University, 10/17/2005 Anatomy of a Au+Au collision time hard parton scattering Au hadronization freeze-out formation and thermalization of quark-gluon matter? Space Time expansion Jet cc   e   pK   

Ralf Averbeck, 13 Stony Brook University, 10/17/2005 electromagnetic radiation: , e + e ,     l rare, no strong interaction → probe all time scales –thermal radiation (black body) → initial temperature –in-medium properties of vector mesons → chiral symmetry restoration hadrons: , K, p, … l abundant, final state –yields, spectra → energy density, thermalization –correlations, fluctuations, azimuthal asymmetries → collective behavior Different probes tell different stories  cc JJ       q q ee ee  “hard” probes: jets, heavy quarks, direct  l rare, produced initially (before quark-gluon matter is present!) –probe hot and dense matter l investigate evolution of a system l that “lives” for ~ s (~100 fm/c) l in a volume ~ m 3 (~1000 fm 3 ) l with energy ~6 x J (~40 TeV)    p     p 

Ralf Averbeck, 14 Stony Brook University, 10/17/2005 one particle ratio (e.g. p/p) determines  B /T a second ratio (e.g.  /p) then determines T l predict all other hadron abundances and ratios l do the huge yields of various hadron species in the final state reflect a THERMAL distribution? l abundances in hadrochemical equilibrium Final state hadrochemistry spin isospin degeneracy temperature at chemical freezeout baryochemical potential l momentum spectra indicate kinetic equilibrium

Ralf Averbeck, 15 Stony Brook University, 10/17/2005 Phase diagram of “nuclear” matter l final state at RHIC: hadronic black body in kinetic and chemical equilibrium l very close to phase boundary between hadronic and quark-gluon matter  B → 0 means B/B → 1 (early universe) l T = 177 MeV provides lower limit for initial temperature l necessary condition for phase transition are met at RHIC!

Ralf Averbeck, 16 Stony Brook University, 10/17/2005 g g medium A view behind the curtain l “tomography” with scattering experiments Rutherford:  → atom  discovery of the nucleus l SLAC: electron → proton  discovery of quarks l calibration of hard probes l theoretically –perturbative QCD (pQCD) l experimentally –measurement in p+p –in-situ control: photons l “tomography“ at RHIC l problem: short life time l probe has to be “auto generated” early in the collision l hard parton (quark, gluon) scattering l scattered parton probes medium, fragments into hadrons –high p T jets –heavy quark probes

Ralf Averbeck, 17 Stony Brook University, 10/17/2005 Direct photons at √s NN = 200 GeV l photons from quark-gluon Compton scattering p-p Au-Au l direct photons are a calibrated probe N binary : number of binary collisions determined event-by- eventfrom collision geometry l no strong final state interaction

Ralf Averbeck, 18 Stony Brook University, 10/17/2005  0 in p-p peripheral N binary = 12.3  4.0 central N binary = 975  94 Au-Au Hadrons  0  at √s NN = 200 GeV l pQCD is (again) in reasonable agreement with p+p data binary collision scaling works for  0 in peripheral Au+Au l strong suppression at high p T in central collisions: energy loss of hard scattered parton in medium?

Ralf Averbeck, 19 Stony Brook University, 10/17/2005 Or is the production suppressed? l saturation of parton density in nucleus at high energy? (not here: direct photon data!) l control experiment: d+Au at √s NN = 200 GeV l nuclear modification factor: High p T hadrons are suppressed in the hot medium at RHIC!

Ralf Averbeck, 20 Stony Brook University, 10/17/2005 l charm: m c ~ 1.3 GeV; bottom: m b ~ 4.5 GeV l produced as quark-antiquark pair hard process (m q >>  QCD ) –pQCD applicable at low p T ! l most pairs separate and form “open heavy flavor”: l charm: D mesons; bottom: B mesons l thermalization, energy loss mechanism l bound states (quarkonia) can be formed as well: charm: J  ; bottom:  l hadronic ↔ quark-gluon matter Heavy quarks: the other hard probe D mesons,  ’, 

Ralf Averbeck, 21 Stony Brook University, 10/17/2005 l ideal (but difficult, in particular in Au+Au) full reconstruction of decays, e.g. How to measure open heavy flavor? l alternative (but indirect) l semileptonic decays contribute to lepton spectra D0  K+ -D0  K+ - MesonD ± (D 0 ) Mass1.87 (1.87) GeV BR D 0 --> K  (3.85 ± 0.10) % BR D --> e +X17.2 (6.7) % BR D -->  +X 17.2 (6.6) %

Ralf Averbeck, 22 Stony Brook University, 10/17/2005 e ± from heavy flavor l many sources contribute to the e ± spectrum l background subtraction l calculation of e ± cocktail from all known (measured) sources l direct measurement of the dominant background –Dalitz decay of    –conversion of photons in material –converter technique l excess beyond background  semileptonic decays of heavy flavor 200 GeV PHENIX: hep-ex/

Ralf Averbeck, 23 Stony Brook University, 10/17/2005 l electrons from heavy flavor decays at mid rapidity l PYTHIA: LO pQCD l FONLL: Fixed Order Next-to-Leading Log pQCD (M. Cacciari, P. Nason, R. Vogt hep-ph/ ) Reference: pQCD comparison l p T < 1.5 GeV/c: pQCD works l p T > 1.5 GeV/c: pQCD “softer“ than data l fragmentation hard? l bottom enhanced? l higher order contributions? l heavy quarks from fragmentation of light quark or gluon jets? l crucial: rapidity dependence (PHENIX  data at  = -1.65) PHENIX: hep-ex/

Ralf Averbeck, 24 Stony Brook University, 10/17/2005 PHENIX PRELIMINARY 1/T AB EdN/dp 3 [mb GeV -2 ] Cold nuclear matter effects l e ± spectrum from heavy flavor decays in d+Au at 200 GeV l data divided by nuclear overlap integral T AB (binary collision scaling assumption) l scaled d+Au data are consistent with fit to p+p reference l agreement holds for various d+Au centrality classes NO indication for significant medium effects in cold nuclear matter!

Ralf Averbeck, 25 Stony Brook University, 10/17/2005 PHENIX: PRL 94, (2005) Hot matter: charm yield in Au+Au l spectra of e ± from heavy flavor decays for different centralities (from converter analysis) l p T > 1.5 GeV/c: not enough statistics to address modification of spectral shape total yield for p T > 0.8 GeV/c l total yield in Au+Au follows binary collision scaling (as expected for hard probe)!

Ralf Averbeck, 26 Stony Brook University, 10/17/2005 Nuclear modification of e ± spectra l cocktail analysis of full statistics data sample (Run-2) l strong modification of heavy flavor e ± spectra is evident at high p T ! PHENIX: nucl-ex/0510???

Ralf Averbeck, 27 Stony Brook University, 10/17/2005 Centrality dependence of e ± R AA l preliminary analysis of Run-4 data sample (~10 9 events!) l clear indication for stronger high p T suppression in more central collisions l collision centrality and “opaqueness” of the medium are related

Ralf Averbeck, 28 Stony Brook University, 10/17/2005 Theory vs. data l energy loss via induced gluon radiation in vacuum: gluon emission suppressed in “dead cone“ (  < m/E) ( Dokshitzer, Kharzeev: PLB 519(2001)199 l in medium: “dead cone“ filled by medium induced radiation (Armesto et al.: PRD 69(2003)114003) (3) q = 14 GeV 2 /fm (2) q = 4 GeV 2 /fm (1) q = 0 GeV 2 /fm (4) dN g / dy = 1000 l data favor models with large parton densities and strong coupling l major uncertainty: contribution from bottom decays at high p T l curves (1-3) are for charm decays only (Armesto et al.: PRD 71 (2005) ) l curve 4 includes bottom decays (M. Djordjevic et al., PRL 94 (2005) )

Ralf Averbeck, 29 Stony Brook University, 10/17/2005 Towards higher p T l bottom decays should dominate the e ± spectrum above p T ~ 5 GeV/c l bottom energy loss < charm energy loss l R AA should rise again l preliminary STAR e ± data l consistent within errors for p T < 5 GeV/c l p T reaches 10 GeV/c l R AA stays small!!!! l large bottom energy loss? l reduced bottom production? l other e ± sources? l experimental problems?

Ralf Averbeck, 30 Stony Brook University, 10/17/2005 l elliptic flow l spatial anisotropy in initial stage l momentum anisotropy in final stage l elliptic flow strength l hydrodynamic calculations measured v 2 of hadrons requires thermalized matter at  5 GeV/fm 3 Does charm thermalize? l R AA << 1 → strong interaction of charm quarks with medium l large charm mass implies long thermalization time scale l unless medium is super dense quark-gluon matter l does charm participate in collective motion?! pYpY pXpX Y X Z Reaction plane: Z-X plane High pressure Low pressure asymmetric pressure gradients (early, self quenching)

Ralf Averbeck, 31 Stony Brook University, 10/17/2005 Heavy quark elliptic flow l PHENIX: significant v 2 rising to p T ~2 GeV/c, but drops for p T >2 GeV/c (bottom contribution) l STAR: significant, almost constant v 2 above p T ~2 GeV/c l v 2 of e ± from heavy flavor from PHENIX & STAR are not consistent l parton thermalization? l most likely, but what happens to heavy quarks at high p T ??? V. Greco et al. PLB 595(2004)202 l theory curves from recombination model (V. Greco et al., PLB 595(2004)202) l non-flowing c quark coalesces with flowing light quark to form a D meson l c quark fully participates in partonic flow

Ralf Averbeck, 32 Stony Brook University, 10/17/2005 ~ 1% of cc forms bound state: J/  (m~3.1 GeV) “easy” to detect: J/  → l + l -, l=e,  (BR~6%) color screening in quark-gluon medium  J/  suppression (Matsui und Satz, PLB176(1986)416) Bound cc states: J/  l central Pb+Pb collisions at SPS (√s NN ~ 17 GeV) J /  suppression beyond “normal” nuclear absorption (NA50: PLB477(2000)28) l perspectives at RHIC l large charm yield additional J /  enhancement via cc coalescence? l key quark-gluon matter probe! l crucial first steps l reference measurement in p+p l cold nuclear matter effects in d+Au

Ralf Averbeck, 33 Stony Brook University, 10/17/2005 J/  at RHIC l factor ~3 suppression l relative to binary scaled p+p in central collisions l data show same trends for l Cu+Cu l Au+Au l e + e - (|y|<0.35) l  +  - (1.2<|y|<2.2) l 200 GeV l 62 GeV

Ralf Averbeck, 34 Stony Brook University, 10/17/2005 Theory comparison: cold matter l cold nuclear matter model (R. Vogt: nucl-th/ ) l in agreement with d+Au data l shows trend to under predict suppression in central Au+Au collisions J/  →  +  - J/  → e + e -

Ralf Averbeck, 35 Stony Brook University, 10/17/2005 Theory comparison: hot matter l models consistent with SPS data l fail to describe RHIC data l too much suppression l models with regeneration mechanism l reasonable agreement l tests (still inconclusive) l p T and y dependence

Ralf Averbeck, 36 Stony Brook University, 10/17/2005 l dileptons (e + e - ) l probe the full time evolution of the collisions l unaffected by strong final state interaction l the “ultimate” tool to look “inside” l measure the full dilepton continuum l main difficulty combinatorial background, e.g. via  →e + e - and  0 →  e + e - More fun with dileptons Thermal radiation Chiral symmetry restoration continuum enhancement modification of vector mesons thermal production or energy loss suppression (enhancement )

Ralf Averbeck, 37 Stony Brook University, 10/17/2005 l e + e - pairs in Au+Au at 200 GeV (~0.8x10 9 events) l foreground: form all e + e - pairs within one event l combinatorial background: from “event mixing” (combine e + from one event with e - from other event) l signal = foreground - background Dielectron continuum at RHIC l systematic error dominated by uncertainty in background normalization: 0.25% !!

Ralf Averbeck, 38 Stony Brook University, 10/17/2005 l e + e - data agree within uncertainties with l cocktail from hadronic sources l charm from PYTHIA (LO pQCD without medium effects) hint for enhancement below  region l charm?? l energy loss l angular correlation? l systematics need to be reduced! Comparison with expectation

Ralf Averbeck, 39 Stony Brook University, 10/17/2005 Summary l a new phase of matter is produced in Au+Au collisions at RHIC l it is hot l it is dense l it has degrees of freedom that are not color-neutral l it is strongly coupled l effective tools to probe the sQGP are at hand l penetrating probes l autogenerated probes from hard scattering –high p T jets –heavy quarks l electromagnetic probes –dilepton continuum –thermal radiation sQGP

Ralf Averbeck, 40 Stony Brook University, 10/17/2005 RHIC The future is bright: RHIC l baseline l detailed system size and energy dependence of now established probes –threshold for sQGP formation? –mechanism of hadronization? l characterization of sQGP properties l PHENIX upgrades and RHIC-II ( ) l HBD (“Hadron Blind Detector“) → Dalitz & conversion background rejection for single e ± and e + e - pairs l SVT (“Silicon Vertex Tracker” → Sekundärvertex (c,b) l RHIC-II (40 x design luminosity) →  (bb) spectroscopy

Ralf Averbeck, 41 Stony Brook University, 10/17/2005 And elsewhere l highest temperature / lowest baryon density  CERN l moderate temperature / highest baryon density  GSI l continue exploration of strongly interacting matter under extreme conditions at next frontiers

Ralf Averbeck, 42 Stony Brook University, 10/17/2005 l thermal radiation with T>>T C would prove beyond any doubt the presence of a quark-gluon black body l competition with photon emission from l hadron gas initial pQCD processes (direct  ) Approaching the “Holy Grail” Turbide, Rapp, Gale: PRC69(2004) l promising window 1 < p T < 3 GeV/c l “real” photons l signal/background currently too small for significant measurement l “virtual” photons ANY source of real photons emits also virtual photons:  0 →  and Dalitz decay:  0 →   →  e + e -

Ralf Averbeck, 43 Stony Brook University, 10/17/2005 l virtual photon spectrum at low mass is known EXACTLY (from QED): Dalitz pair mass spectrum Dalitz pairs and virtual photons phase-space factor →1 for high p T  el.magn form factor →1 for small m ee l shape analysis of low mass e + e - spectrum no thermal radiation → shape must agree with expectation from  0 and  Dalitz decays excess → direct  * l then calculate  * direct /  * inclusive

Ralf Averbeck, 44 Stony Brook University, 10/17/2005 l significant direct virtual photon signal observed l trend towards stronger signal in more central events translate into “real” photon spectrum  direct =  incl. (  * dir. /  * incl. ) l with  incl. being the measured inclusive “real” photon spectrum  * direct /  * inclusive

Ralf Averbeck, 45 Stony Brook University, 10/17/2005 l data are consistent with expectation from l direct photons from hard scattering (pQCD·T AB ) (Gordon, Vogelsang: PRD48(1993)3136) l thermal radiation from quark-gluon matter (d’Enterria, Perresounko: nucl-th/ ) –hydrodynamical model –T 0 = 590 MeV –t 0 = 0.15 fm/c l thermal radiation? l reference data from p+p and d+Au are needed first! Direct (thermal?) photon yield

Ralf Averbeck, 46 Stony Brook University, 10/17/2005 The PHENIX Collaboration

Ralf Averbeck, 47 Stony Brook University, 10/17/2005 How rare is charm at RHIC? l production cross section at RHIC:  cc ≈ 1 mb in p+p l assume binary collision scaling (hard probe) l central Au+Au collision: ≥ 20 cc (if NO medium effects)!

Ralf Averbeck, 48 Stony Brook University, 10/17/2005 1/T AB 1/T AB EdN/dp 3 [mb GeV -2 ] Centrality (in)dependence in d+Au